This invention relates generally to improvements in fastener driving tools, and specifically to such tools designed to utilize fastener of varying sizes. The present tool automatically adjusts to different sized fasteners to reduce jamming, making the tools easier to use and having more accurate fastener delivery.
Power framing tools for use in driving fasteners into workpieces are well known. The framing tools are usually portable and are powered pneumatically or by combustion. Similar pneumatic tools are described in U.S. Pat. Nos. 4,932,480; 3,552,274 and 3,815,475, all of which are incorporated by reference. Combustion powered tools are described in commonly assigned patents to Nikolich, U.S. Pat. Nos. Re. 32,452; 4,403,722; 4,483,473; 4,483,474; 4,552,162; 5,197,646 and 5,263,439, all of which are incorporated herein by reference. Such combustion powered tools particularly designed for trim applications are disclosed in commonly assigned U.S. Pat. No. 6,016,622, also incorporated by reference herein. Similar combustion powered nail and staple driving tools are available from ITW-Paslode under the IMPULSE(copyright) brand.
Such tools incorporate a generally pistol-shaped tool housing enclosing the power source, such as a pneumatic cylinder or a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas also called a fuel cell. Power is generated from expansion of compressed gasses, either by burning of fuel in a combustion chamber or expansion of air in the pneumatic cylinder. The power source moves a reciprocating piston having an elongate, rigid driver blade disposed within a piston chamber of a cylinder body. A safety interlock prevents firing of the tool unless a workpiece contact element at the end of a nosepiece, or nosepiece assembly, is pressed against a workpiece.
Upon the pulling of a trigger, gas or air expansion causes the piston and the driver blade to be shot downward to impact a positioned fastener and drive it into the workpiece. As the piston is driven downward, a displacement volume enclosed in the piston chamber below the piston is forced to exit through one or more exit ports provided at a lower end of the cylinder. After impact, the piston then returns to its original or xe2x80x9creadyxe2x80x9d position through differential gas pressures within the cylinder. Fasteners are fed into the nosepiece barrel from a supply assembly, such as a magazine, where they are held in a properly positioned orientation for receiving the impact of the driver blade. The fasteners are then propelled through the length of the barrel by the driver blade, exiting the barrel at the workpiece surface. Force of the driver blade and the momentum of the fastener drives the fastener to penetrate the workpiece.
Framing tools are commonly used in residential construction primarily for driving nails into wood. Metal hardware pieces, such as joist hangers, connecting plates and seismic strapping are frequently attached to the wood framing requiring relatively accurate placement of the fastener in openings or slots in the metal hardware. A POSITIVE PLACEMENT(copyright) tool is a specialty framing tool that is used where accurate placement of the fastener is desirable. This tool has a probe that aids alignment of the fastener with the hardware openings.
At least two different lengths of nail, 1xc2xdxe2x80x3 and 2xc2xdxe2x80x3, are typically used for these applications. Current designs for these tools require the user to change settings on the tool when changing between different nail lengths. The user must first pull on a spring-biased plunger to disengage it from a rebound lever. The rebound lever pivots approximately 60 degrees about a pin. While holding the plunger in the outward position, the lever must be rotated via the handle to the other position. When the plunger is released, it again engages with the lever to lock it into the new position. Such an operation requires two hands, one to hold the tool and the other pull the plunger, rotate it and allow it to reengage. In construction environments, the user is often in an inconvenient place, trying to align two or more workpieces to be fastened together. It is not always practical to free both hands to effect the setting change.
In currently available tools, there is also no mechanism for prohibiting the user from loading short nails into the magazine when the lever is set for the long nails. When set for long nails, there is a longer opening to the nosepiece permitting entry of the nail. If the tool is operated in this condition, the short nails can rotate before they travel the length of the opening, causing a jam. The driving mechanism can become wedged between the nail and the nosepiece, causing it to become stuck and rendering the tool inoperable. This condition has been the cause of many field failures of the tool.
Rotation or tumbling of a short nail as it is being driven also leads to inaccuracies in the flight of the nail. Dimensional differences of the fasteners allow more freedom of movement of smaller fasteners within the barrel. Lateral movement of the nail as it travels down the barrel permits the nail to exit the barrel at random orientations compared with the vertical axis of the barrel. Precise nail placement is attained when the fasteners travel a consistent path through the nosepiece. Reduction of rotation of the nail results in better nail control, allowing more accurate nail placement.
The problem of accuracy when using short fasteners is addressed in U.S. Pat. No. 6,279,808 to Larsen, herein incorporated by reference. Larsen discloses a two-piece nail gun guide having a biased arm that protrudes into the barrel, exerting a force on each nail as the nail travels down the barrel and passes by the arm. The biasing force of the arm pushes each nail to one side of the nail gun barrel, increasing the accuracy and consistent orientation of the nail as it exits the barrel. However, this mechanism exerts the biasing force on the fastener as it exits the nosepiece, not as it enters the barrel. It does not prevent jamming of short fasteners due to tumbling as they enter the barrel. Nor does this reference teach or imply that the nail guide serves as an automatic adjustment for fasteners of differing lengths.
Another difficulty with current nosepiece designs is the potential for build-up of collation paper in the barrel. Generally, when the driver blade contacts the fastener, propelling it through the barrel and into the workpiece, the fastener is rapidly torn from the collation paper. The paper may continue to cling to the fastener, or it may remain attached to the subsequent fastener. If portions of the paper are carried through the barrel with the fastener, it will come loose and immediately be dispersed with the fastener penetrates the workpiece. However, sometimes the paper is pushed aside by the fastener and driver blade and remains attached to the next fastener. When this occurs the collation paper can prohibit this next fastener from fully entering the barrel. Firing the tool in this condition results in poor nail control and may result in a jam.
It is an object of the present invention to provide an improved fastener driving tool which adjusts to varying fastener size without requiring manual intervention from the user.
Another object of this invention is to provide an improved fastener driving tool with more accurate placement of short fasteners.
Still another object of this invention is to provide an improved fastener driving tool that reduces jamming of the fastener in the nosepiece.
Yet another object of this invention is to provide an improved fastener driving tool that allows collation paper to be removed from the barrel of the tool before it jams.
These and other objects are met or exceeded by the present invention which features a nosepiece and shear block assembly that automatically adjusts the length of the nosepiece barrel to accommodate fasteners of differing sizes.
More specifically, the present invention provides a nosepiece and shear block assembly for a fastening tool that drives a fastener supplied from a plurality of fasteners. The assembly includes a nosepiece that is configured for attachment to the tool and defines a portion of a barrel and a shear block configured to be secured to the nosepiece to complete the barrel. There is an opening in the barrel for receiving a fastener. The assembly also includes a biased fastener-size adjustment device, which exerts a biasing force against fasteners adjacent the opening.
In a preferred embodiment of the invention, the nosepiece and shear block assembly is supplied with fasteners removably attached to a collation tape. At least one window in the nosepiece is aligned with the path of the coalition tape, and permits removal of the tape when the fastener enters the barrel.
The fastener driving tool of the present invention provides automatic adjustment of the opening to the barrel in response to the length of the fastener. Allowing the fastener-size adjustment device, such as a rebound lever, to pivot about a point and biasing it toward the fastener, it automatically adjusts to the fastener length. There is no need for the user to pull on a plunger while attempting to hold on to the tool, rotate the rebound lever, and then release the lever to lock it into the new position. More importantly, the present fastener adjustment feature further eliminates jamming of the tool if the user changes fasteners and forgets to move the position of the rebound lever. The new tool is also particularly useful in operational environments where it is difficult to find a place to rest the tool to effect the change. The present adjustment mechanism provides for continuous size adjustment between a shortest size and the longest fastener that will be accommodated by the barrel opening.
Accuracy of placement for short nails is also improved by the present invention. Movement of the rebound lever to cover the portion of the opening not used by short fasteners prevents them from bouncing off the barrel walls and into the shear block. This provides a straighter path and allows the nails to rotate less within the barrel, allowing for more consistent placement of the nails.
At least one, and preferably a plurality, of windows placed in the nosepiece provides an outlet for the collation tape upon which the fasteners are assembled. If the tape is not expelled with the fastener, the use of windows prevents build-up of tape in the barrel or the nosepiece. Aligning of the windows where the paper tape typically intersects with the portion of the barrel wall allows the tape to exit without accumulating and allows the next nail to entirely enter the barrel of the nosepiece until the nail head and shank makes contact with the surface of the barrel opposite of the opening.